content: /* Copyright (C) 2016-2018 Alibaba Group Holding Limited
  
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at
  
      http://www.apache.org/licenses/LICENSE-2.0
  
  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
  ==============================================================================*/
  
  // Protocol Buffers - Google's data interchange format
  // Copyright 2008 Google Inc.  All rights reserved.
  // https://developers.google.com/protocol-buffers/
  //
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are
  // met:
  //
  //     * Redistributions of source code must retain the above copyright
  // notice, this list of conditions and the following disclaimer.
  //     * Redistributions in binary form must reproduce the above
  // copyright notice, this list of conditions and the following disclaimer
  // in the documentation and/or other materials provided with the
  // distribution.
  //     * Neither the name of Google Inc. nor the names of its
  // contributors may be used to endorse or promote products derived from
  // this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  package com.google.protobuf;
  
  /**
   * Abstract base interface for protocol-buffer-based RPC services.  Services
   * themselves are abstract classes (implemented either by servers or as
   * stubs), but they subclass this base interface.  The methods of this
   * interface can be used to call the methods of the service without knowing
   * its exact type at compile time (analogous to the Message interface).
   *
   * <p>Starting with version 2.3.0, RPC implementations should not try to build
   * on this, but should instead provide code generator plugins which generate
   * code specific to the particular RPC implementation.  This way the generated
   * code can be more appropriate for the implementation in use and can avoid
   * unnecessary layers of indirection.
   *
   * @author kenton@google.com Kenton Varda
   */
  public interface Service {
    /**
     * Get the {@code ServiceDescriptor} describing this service and its methods.
     */
    Descriptors.ServiceDescriptor getDescriptorForType();
  
    /**
     * <p>Call a method of the service specified by MethodDescriptor.  This is
     * normally implemented as a simple {@code switch()} that calls the standard
     * definitions of the service's methods.
     *
     * <p>Preconditions:
     * <ul>
     *   <li>{@code method.getService() == getDescriptorForType()}
     *   <li>{@code request} is of the exact same class as the object returned by
     *       {@code getRequestPrototype(method)}.
     *   <li>{@code controller} is of the correct type for the RPC implementation
     *       being used by this Service.  For stubs, the "correct type" depends
     *       on the RpcChannel which the stub is using.  Server-side Service
     *       implementations are expected to accept whatever type of
     *       {@code RpcController} the server-side RPC implementation uses.
     * </ul>
     *
     * <p>Postconditions:
     * <ul>
     *   <li>{@code done} will be called when the method is complete.  This may be
     *       before {@code callMethod()} returns or it may be at some point in
     *       the future.
     *   <li>The parameter to {@code done} is the response.  It must be of the
     *       exact same type as would be returned by
     *       {@code getResponsePrototype(method)}.
     *   <li>If the RPC failed, the parameter to {@code done} will be
     *       {@code null}.  Further details about the failure can be found by
     *       querying {@code controller}.
     * </ul>
     */
    void callMethod(Descriptors.MethodDescriptor method,
                    RpcController controller,
                    Message request,
                    RpcCallback<Message> done);
  
    /**
     * <p>{@code callMethod()} requires that the request passed in is of a
     * particular subclass of {@code Message}.  {@code getRequestPrototype()}
     * gets the default instances of this type for a given method.  You can then
     * call {@code Message.newBuilderForType()} on this instance to
     * construct a builder to build an object which you can then pass to
     * {@code callMethod()}.
     *
     * <p>Example:
     * <pre>
     *   MethodDescriptor method =
     *     service.getDescriptorForType().findMethodByName("Foo");
     *   Message request =
     *     stub.getRequestPrototype(method).newBuilderForType()
     *         .mergeFrom(input).build();
     *   service.callMethod(method, request, callback);
     * </pre>
     */
    Message getRequestPrototype(Descriptors.MethodDescriptor method);
  
    /**
     * Like {@code getRequestPrototype()}, but gets a prototype of the response
     * message.  {@code getResponsePrototype()} is generally not needed because
     * the {@code Service} implementation constructs the response message itself,
     * but it may be useful in some cases to know ahead of time what type of
     * object will be returned.
     */
    Message getResponsePrototype(Descriptors.MethodDescriptor method);
  }
  